Many academic and commercial projects have generated combinatorial libraries of small molecules, nucleic acids, or proteins. Screening through these libraries will result in the identification of novel compounds of interest to basic science and medicine. However, automated high-throughput methods currently exist only for very simple systems (e.g., in vitro assays or single cells). Thus, the current state of the art makes it difficult or impossible to conduct high-throughput screens in complex organisms or to conduct screens to identify and/or characterize compounds which affect higher-order behavioral, morphological, or anatomical characteristics in complex organisms.
The current state of the art regarding screening assays in complex organisms is also limited in other respects. Even assays of single candidate compounds or of a small number of candidate compounds can be difficult when conducted in complex organisms. Specifically, assays based on making multiple observations of a complex organism over time are prone to experimenter bias, error, and fatigue. This problem is exacerbated when attempts to scale-up such a screen are made.
The limitations of the current state of the art are perhaps most acutely, although certainly not exclusively, experienced when the observational endpoint of the screening assay is a metric such as learning or memory. Such cases represent perhaps the most complex of animal behavior. Furthermore, assays that chart changes in learning or memory typically require the gathering and analysis of data points over time, thus exacerbating the potential that experimenter bias, error, or fatigue will influence the results.
An important aspect of biology is the discovery of novel genes, proteins, or chemical reagents that have interesting, useful, and/or enlightening effects upon living systems. We appear to be leaving the classical era where these were mainly discovered fortuitously (e.g., most antibiotics and neurotoxins), but are still fairly far from the generalized ability of rational design of drugs or proteins, linking structure to desired function at will (Debouck and Metcalf (2000) Annul Rev Pharmacol Toxicol 40: 193-207; Farber (1999) Pharmacol Ther 84: 327-332). Thus, current efforts are focused on screening approaches: locating interesting reagents by large-scale high-throughput examination of candidate molecules present, for example, in a combinatorial library (Bensing et al. (2001) Infect Immun 69: 1373-1380; Cheung et al. (2002) Nature Cell Biol 4: 83-88; Goodnow (2001) J Cell Biochem Supp 37: 13-21; Katayama et al., 2001; Koide et al. (2001) J Am Chem Soc 123: 398-408; MacNeil et al. (2001) J Mol Microbiol Biotechnol 3: 301-308; Nuttall (2001) Cells Tissues Organs 169: 265-271). A number of academic and commercial pharmaceutical projects have generated large genetic, proteomic, or small-molecule (drug) libraries that must be screened to identify compounds of interest to both biomedicine and basic biology (Stephen et al. (2002) Biochem Biophys Res Comm 296: 1228-1237), or proteins which alter specific patterning events in developing embryos (Caveman (2000) J Cell Sci 113: 3543-3544; Colaiacovo et al. (2002) Genetics 162: 113-128; Cram et al. (2003) J Cell Sci 116: 3871-3878; Gonczy et al. (2000) Nature 408: 331-336; Lee et al. (2003) Nucleic Acid Research 31: 7165-7174; Thatcher et al. (2001) Develop Biol 229: 480-493; Tseng and Hariharan (2002) Genetics 162: 229-243; Vastenhouw et al. (2003) Current Biol 13: 1311-1316).
There is an endless list of potential targets for which screening of libraries would result in medically-valuable reagents, or perturbation of biological processes which then lead to increased basic understanding of endogenous control mechanisms. Generating the libraries is often easy; the crucial and usually most difficult aspect is the choice of screening methods, apparatuses, and systems. This requires a tractable yet relevant model system, a degree of automation (to ensure temporal and financial feasibility), and a test which gives useful answers for each candidate. Some screens have been successfully conducted using cell culture or unicellular organisms (e.g. bacteria or yeast) (Chen and Zhao (2003) Gene 306: 127-134). Large-scale screens in model systems such as mice are not feasible due to cost constraints and the resulting low sample size.
The foregoing illustrate examples of some of the limitations of the prior art. The present invention addresses these and other limitations, and provides apparatuses, systems, and methods for conducting assays in animals.